To accelerate adoption of PHP 5.6 and PHP 7, WordPress should end of line support for older PHP on newer versions of WordPress. WordPress offers security updates of WordPress all the way back to 3.7 whose most recent release was on 6 March 2017 (3.7.19). There's a beautifully maintained download page for all past releases. Ironically they print this nonsense at the top of the secure versions download page:

This is an archive of every release we’ve done that we have a record of. None of these are safe to use, except the latest in the 4.7 series, which is actively maintained.

This simply not true. There's no reason a PHP 5.2 user couldn't safely remain on WordPress 4.4 or WordPress 4.6 whose most recent releases were also on 6 March 2017. We created a plugin BusinessPress to allow a user to safely enable security updates without participating in ever major upgrade. It works a treat. WordPress could do something similar for users on older versions of PHP.

With his constant talk of market share, Matt Mullenweg seems unwilling to put at risk a small amount of market share to do the right thing for the platform. And that would be to make future versions of WordPress PHP 5.6 and PHP 7 only. Recently I've had developers quit as they are tired of working with out of date technology (specifically referring to PHP 5.2, 5.3 and 5.4).

When WordPress loses the developers, WordPress will lose the customers. Long time WordPress advocates and design frontrunners Smashing Magazine have already lost patience with WordPress and moved to jamstack. It's high time to stop worrying about today's marketshare and start worrying about tomorrow's WordPress.

The logical step would be to leave PHP 5.2, 5.3 and 5.4 behind on the next release with 5.5 soon to follow.